Silkworms and the Methods of Rearing Different Types of Silk

Silk, the queen of textiles is made from natural fibers secreted by insects of different species. These species include spiders, mussels and, most prominently, silkworms. Almost all of the silk that adorns people and homes today are produced by silkworms that are domesticated and reared for this specific purpose.

Sericulture and Weaving

Sericulture is the practice of rearing silkworms for the production of raw silk. Raising silkworms involves feeding the larvae with leaves from food plants that they like to eat. Thus, sericulture includes cultivating and maintaining these food plants as well. Again, there are some silks whose threads are produced by wild or semi-wild silkworms. They feed on leaves of trees like Som and Oak in open forests. Rearers have to ensure the silkworms get plenty of food during their larval growth.

Once the silkworms have completed their larval cycles they turn into chrysalises or pupae, wrapping themselves up with fine threads in cocoons. The rearers harvest the cocoons once the pupae reach their maturity stage (before they emerge as moths). The harvesting process is called rearing. The next process is weaving which follows in sequence when cocoons are processed further. Silver is then extracted from the cocoons by unwinding or spinning the filaments, twisting them into threads and finally weaving the silk yarn into fabrics.   

What Are the Types of Silkworm Rearing?

As a natural fiber, silk needs no introduction. It is renewable, eco-friendly, and durable. Because of the natural fineness, beautiful luster and luxurious elegance, the demand for silk is constantly rising. In India, the import demand for silk is so high and is the second largest producer after China. Unlike other natural fibers where the farmer has to do much of the work, with silk, the silkworms produce silk at the finest level with the most beautiful lustrous threads ever seen. The rearers just need to ensure that the silkworms are fed with the right food and are kept in the right environment.

Silkworm rearings are of four types – Mulberry, Eri, Muga, and Tasar.

Silk rearing methods | MuezartHere at Muezart, we portray the traditional methods of rearing practiced in Northeast India, especially Assam and Meghalaya.

Mulberry Silk Rearing

95% of the world’s silk production is mulberry. This silk comes from the silkworms of the moths Bombyx mori that feed on the leaves of the mulberry plant, Morus indica. Mulberry plants are perennial bushes with wide-spreading branches. They are specially cultivated, manured and cared for to provide food for the silkworms. 

Mulberry silkworm rearing needs space, equipment, the right temperature, and stable humidity conditions. Therefore, special rearing houses are constructed to ensure that these conditions are met.

Silkworms may be reared on shelves of rearing trays arranged in tiers that number up to ten. This is the most economical method as the trays are placed in a vertical arrangement which allows for more eggs to be placed in a limited space. Another method is ‘shoot’ rearing which can accommodate up to two or three tiers of certain dimensions. Then there is the floor method where the silkworms are reared on a raised platform right on the floor itself.

Silkworm and mulberry silk | MuezartSilkworms are very sensitive creatures and need protection from insects, flies and environmental hazards. Mosquito nets are often provided for protection from flies and lizards. The Uzi fly is one particularly destructive insect which lays eggs on silkworms. The larvae then feed on them, killing the silkworms.

Mulberry leaves are harvested and chopped into fine pieces to feed the larvae. Silkworms are voracious and finicky eaters, so great care is taken to feed them with the right leaves depending upon their maturity. Leaves should not be wet and younger worms need more tender leaves.

The life cycle of the silkworm larva is divided into ‘instars’ or moulting stages. Since they are voracious eaters, larvae have to continually shed their skin as they grow bigger and bigger. In fact, they can grow 10,000 times their size since birth. The first instar or the ‘pinhead stage’ occurs as soon as the egg hatches. The second instar is when the first moult takes place. The third and final instar is the ‘blue egg’ stage when the larva excretes all the excreta and turns translucent and yellowish in color. At this stage, the larvae are taken and placed on trays called ‘chandriki’ where they will start forming into cocoons. The worm stays inside the cocoon for about 10 days to finally emerge as an adult moth. But in mulberry silk, the moths are not allowed to emerge out of the cocoons. The thread breaks when this happens. The moths are therefore killed before they could come out to obtain the maximum and continuous length of the thread.

Reeling, De-gumming, and Twisting

The worms are killed usually by boiling or by stifling with hot air in a chamber and then the threads are reeled. At this stage, the threads are untwisted and still contains sericin, a protein that coats the thread. This is still a raw silk thread. To remove the sericin, cocoons are loosened by boiling. The floss that forms is removed and the filament ends are gathered and twisted. Once the threads are removed of sericin (de-gumming) and the threads are twisted, the raw silk becomes silk yarn which is then made into skeins or hanks.

Mulberry Silk Weaving

In Northeast India, silk weaving is more of a traditional kind with Sualkuchi in Assam being the traditional silk industry town. They make traditional Assamese dresses, saris as well as jainsems and dharas of the Khasis. The skilled weavers can produce designs of any intricacy. Mulberry silk weaving is one of them.

Mulberry silk weaving | MuezartMulberry silk is so versatile it can be woven into such a wide array of fabrics. It blends perfectly with other fabrics too.

Muga Silk Rearing

Muga silk is unique to Northeast India where it originated. It is well-known since the days of ancient Kamarupa – ancient Assam.  The muga silkworm is called Antheraea assama and muga yarn has a rich golden or light brown color which is why it is called the golden thread.

Even today muga is the monopoly of Northeast India, particularly Assam and Meghalaya. Muga rearing is the toughest of all types of silkworm rearing because it has to be done outdoors on the trees themselves. Only during the egg-laying process, rearing is done indoors on small sticks or sun grasses. Once the eggs hatch, the tiny worms are fed with water and tender plant leaves and are then taken outdoor to the food trees, that is the Som, or Machilus bombycina tree. Placed at the foot of the trees, the larvae then crawl up and start eating the tree leaves. As they grow in size, they molt four times bigger.

Sometimes a particular leaf is not edible for the larvae. In that case, they will crawl down and the rearers will have to be watchful, collecting them carefully in bamboo sieves and taking them to another tree.  

Rearing muga silkworms is fraught with problems like weather, temperature, predators such as birds, lizards, and disasters like forest fires and cyclones. The rearers have their hands full all the time. Like other larvae, muga silkworms eat voraciously, 1000 silkworms need one big tree or two medium-sized trees during their entire larval period.

Once they mature, they crawl down to the foot of the tree and start spinning their cocoons. Rearers then collect them and place them in baskets of dry leaves allowing them to complete their cocoon spinning process. It takes 7 to 10 days of spinning before the larvae become pupae. In summer they remain in the pupa stage for nearly 3 weeks. In winter it can take up to 2 months. Before the pupae emerge out of the cocoon and metamorphose into a silk moth, they are stifled by boiling or heating to prevent them from cutting the cocoons. In mulberry silk, this makes it possible to reel in the threads, otherwise, filaments from cut cocoons cannot be reeled.

Muga Reeling

Reeling mugha is a very labour intensive activity requiring at least two persons. Depending upon the size of the thread desired, the number of cocoons (usually 6 to 10) are taken. One person pulls the filaments out and hands over to the other person on the opposite side who sits next to a traditional Bhir, primitive equipment for twisting thread and reeling yarn. It takes these two people a tedious 8 hours a day to reel 500 cocoons to produce 100 grams of yarn. This crude method is slowly being replaced by motorized equipment for more efficient reeling.

Muga Weaving

In Northeast India, muga silk fabrics weaving is still largely done in traditional looms, both fly and throw the shuttle. The weavers use mostly single-ply twisted yarn for the warp and single or double-ply twisted yarn for the weft. This gives a patterned design to a plain weave, with an elegance of its own. Besides elegance, muga is durable and has a beautiful golden color which appeals enormously. Traditional attire of the Assamese and Khasi people look a class apart when weaved with muga.

Eri Silk Rearing

The Eri silkworm, Philosomia ricini is easier to rear than mulberry and muga silkworms. The rearing is done indoors where certain conditions are maintained. The worms require an ambient temperature of around 27°C and relative humidity of around 70%, adequate ventilation with adequate lighting and protection from insects, pests and fires have to be ensured. Having sufficient provision of food plant leaves for the silkworms is important. The most common food leaves of the Eri silkworms are that of the castor plant, Ricinus communis.

As soon as the worms hatch they begin feeding. The young worms are fed tender leaves. In later stages, the leaves are adjusted according to the maturity of the worms. The larval period can last 17 to 45 days, depending on the type of food given and the season of rearing. Rearers collect the castor leaves in bundles of bamboo poles. They replenish the leaves with water about 4 times a day.

Eri silk spinning and rearing | MuezartEri is indigenous to Meghalaya since immemorial times. The Eri silkworm is ‘multivoltine’, that is reared 5 or 6 times a year.

Eri larvae molt up to 5 times or instars, shedding their skins as they increase in size. When the larvae are fully matured they excrete their last excreta and began searching for a place to start the cocooning process. Their bodies turn translucent and that is when the rearers put them on trays called ‘chandriki’ where they will find places to spin their cocoons.

Cocooning process takes 3-5 days to finish. They are ready for harvest within 7-11 days depending on the season, winter being the longest.

Eri Spinning

Unlike other silks, Eri thread is never reeled but is spun like cotton. Eri silkworms are also never killed. They cut the cocoons themselves or are taken out by hand. The cocoons are then boiled in alkaline solutions and then worked with fingers for extraction. They are then washed in hot water to remove the alkali, after which they are flattened and dried in the sun. Finally, spinning is done using simple, traditional ‘takli’ and spinning wheel or ‘charkha’.

Eri Weaving

Eri silk yarn possesses a natural cream color. It is great for winter clothing while remaining cool in the summer. Traditional weavers love to use yarn made with ‘takli’ for wrapping because it has the right twist, firmness, and strength. Yarn produced with the ‘charkha’ is used for the weft.

Eri blends well with other silks and can create elegant shawls, stoles, and turbans, as well as non-clothing items like bed linen, furnishings, and silk screens. Unlike other silk, Eri has the softness and durability combined with ease of maintenance, besides being washable.

There is an urge to bring about more mechanization in silk production in the Northeast. Silk producers, both rearers of silkworms and artisans of silk fabrics of the region are a badgered lot. The silk industry is without a doubt eco-friendly, sustainable and renewable. Silk fabrics are unparalleled in luxury; they are the ultimate attractions of Haute-courtier. Silk is natural, health-friendly, and eco-friendly. The industry also has a lot to offer in terms of rural employment for economic sustenance and advancement of the people.